This invention relates generally to solid fuel burning heaters. More specifically, it relates to a log or coal burning heater capable of maintaining a uniform heat output for extended times with a single fuel load, and capable of burning fuel completely at extremely slow combustion rates such as when a fire is banked overnight or minimal heat demands are placed on the heater.
Wood and coal burning heaters are, of course, well known. However, it has always been difficult to regulate the amount of air fed to such heaters and to control fuel consumption. Most have been inefficient and dirty, have required re-fueling at short intervals and many would not even hold a banked fire overnight.
Typically, a wood or log burning heater runs very hot at first and then tapers off; and, when the fire is banked for the night, it burns itself out before morning and has to rekindled.
Complete burning occurs in two stages: primary combustion on the grate where logs are converted to smoky, incompletely burned, air-borne particles, carbon monoxide, and the like; and secondary combustion, where the air-borne smoke and carbon monoxide are cleanly converted to carbon dioxide and water and minor quantities of other completely oxidized components. Too little air prevents complete combustion, leaves ashes in the heater, and produces smoke which is highly visible and objectionable. To avoid smoke, a heater is generally oversupplied with air causing rapid combustion and an unnecessary loss of heat into the room and up the chimney. Attempts to restrict and control the air supply to prolong burning at a low rate all too often results in the fire going out.
It is difficult to maintain a banked or low heat output fire with very low flow rates of cold, ambient air. The cold air simply cools the embers and the gases to or below the ignition temperature causing burning to be very inefficient and smoky before it eventually goes out. On the other hand, pre-heating of the air fed to a banked fire enables it to burn completely, even at a very low combustion rate.